The present invention relates to ultrasonic fluid level sensing. In particular, the present invention relates to non-invasive ultrasonic fluid level sensing in an automated diagnostic analyzer.
When containers are used to contain a fluid, such as water, it is desirable to know the level or height of fluid in the container in order to determine the volume of fluid remaining in the container. There are many prior art fluid level sensors that determine the level of fluid in a container. However, most existing fluid level sensors are “intrusive,” which require a sensor to be located inside the container. Because the intrusive fluid level sensors are located inside the container, the sensors are difficult to mount and may be difficult to access for replacement or repair. Intrusive fluid level sensors are also exposed to the contents of the container and pressure inside the container, which can be hazardous to the sensor, and the sensor may contaminate the contents of the container. Finally, some intrusive fluid level sensors require holes to be drilled in the container, which adds additional time and expense to the mounting procedure, and compromises the integrity of the container.
Non-intrusive fluid level sensors may be used in place of intrusive fluid level sensors. The non-intrusive fluid level sensors may use a transducer to send ultrasonic pulses through the container and detect the reflection of the transmitted pulses (an echo pulse) that is generated when the ultrasonic pulses reach a fluid-air (or fluid-gas) interface in the container. By measuring the elapsed time between the emission of the original pulse and the detection of the reflected pulse, and knowing the speed of travel of the pulses in the container, the level of fluid in the container may be determined.
In order to couple the transducer to the walls of the container such that the transducer can transmit ultrasonic pulses through wall of the container, a couplant must be used. Typically, a “wet” couplant, which is a gel or liquid, is used to couple the transducer to the container wall. However, wet couplants can be difficult to handle and to contain inside the sensor. Wet couplants increase the difficulty of mounting and replacing a non-intrusive level sensor because the wet couplant may tend to leak or escape when the sensor is unassembled. Furthermore, a wet couplant has a natural tendency to lose moisture, and thus may dehydrate or dry out over time. U.S. Pat. No. 6,412,344, which is incorporated by reference in its entirety, discloses sensors including dry couplants. However, these sensors are preferably bonded to the tank or bottle. With the sensor bonded to the tank or bottle a quick exchange between bottles is difficult. An ultrasonic non-invasive sensor, the SL-730 Series, is available from Cosense, Inc., Hauppauge, N.Y.
Known diagnostic analyzers include immunodiagnostic analyzers such as the Vitros® ECi immunodiagnostic analyzer, or clinical chemistry analyzers such as the Vitros® 5,1 FS, both sold by Ortho-Clinical Diagnostics, Inc. All such analyzers are collectively called diagnostic analyzers. Representative systems are disclosed for example in U.S. Published Patent Application No. 2003/0026733, U.S. application Ser. No. 10/684,599 filed Oct. 14, 2003, U.S. Published Patent Application No. 2005/0196867, all of which are incorporated herein by reference in their entireties. Such diagnostic analyzers typically have the need to store onboard the instrument reservoirs that contain fluids that are used in the immunoassay reactions. Usually there is a need for a liquid waste container as well. An accurate volume determination for the amount of fluid in these containers is needed for the scheduling of assays.
Most diagnostic analyzers use a type of level sense method that is invasive such as float switches or similar. Floats are in contact with the liquid in the bottles, and during the changing of the fluids, some of the fluids can come in contact with the person changing the bottles or the instrument. Some analyzers use air pressure to sense the level in the bottles. This method has the drawback of taking quite a bit of time to do the volume determination. An ultrasonic dry couplant such as described in the '344 patent would be desirable, except that such a sensor is biased against the container, such as by a spring.
Depending on use, these bottles have to be often changed. Therefore, it would be desirable to have a level sense system that quickly disengages from the bottles for easy replacement.